Purification of lactic acid



Patented June 18, 1940 UNITED STATES PATENT OFFICE PURIFICATION OF LAc'rio Aom Ivan L. Haag and Charles A. Vana, Cleveland, Ohio, assignors to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application October 22, 1937, Serial No. 170,387

5 Claims. (Cl. 260-535) This invention relates to processes for the puristood reference should be had to the followin fication of lactic acid and is more particularly illustrative p directed to processes wherein lactic acid treated Example with nitric acid and containing a cyanide as an 5 impurity is further purified by treatment with a TWO hundred Parts by Weight of fifty Per silver compound. cent solution of edible lactic acid prepared by In an applicatio 10353, fil d March 11 partial purification of lactic acid made by fer- 1935, for Purification of lactic acid of which this mentation of molasses was heated to a temperaapplication is a continuation in part, We have ture of 90 C. To the lactic acid there was added 1 shown processes for the purification of lactic parts by Weight of a seventy per cent 0. P.

i according t which t acid is first treated nitric acid solution. After the addition 0f nitric it nitric acid as an oxidizing agent and then acid the heating was continued for four hours excess nitric acid is removed as by the use of holding the temperature between about 90 and activated carbon or decolorizing carbon. Excess r nitric acid may also be eliminated by the use of The nitric acid-treated tattle acld was heavy base metals such as aluminum or coppen centrated to eighty per cent and there was then The treatment of lactic acid with nitric acid added four parts by weight of activated carbon. to effect purification causes the formation of cy- The mixture a Stirred for three hours at 90 to anides which remain in the lactic acid after treat- The actlvated carbon was then allowedto ment. Chlorine ions are sometimes introduced Settle The clear acid- Was syphoned Off and 20 into the lactic acid by the use of activated carwas again treated using one part/by Weight of bon and remain after treatment as an impurity fresh activated carbonin the lactic asii Iron, which like chlorine is an impurity intro- NOW we have found t t an improved lactic duced by the activated carbon, was precipitated 5 acid may be prepared treating acid from the acid. potassium felIOCyanidB treated lactic acid with a compound of silver. until no further precipitate formed- The lactic By such treatment any cyanides present in the acid W then Separated m the carbon and acid combine with the silver to form an insoluble ates of iron ferrocyamde. precipitate from which the lactic acid may read- The 13431710 361d Solutlon contammg cyamdes n ily be separated. Chlorine and other such impu- P incipally in the form of hydrogen cyanide was rities, if present, will also be separated by the then further purified y adding Silver te 1 combination with silver to form an insoluble pretil no further precipitate was Obtained- Chlorine cipjta te of course was precipitated at the same time.

According to the processes of our present in- The lactic acid was separat d f o the p p vention, lactic acid which has been treated'with tate by decanting- An a ys s S owed that Subnitric acid and from which excess of nitric acid Stantially 601111919196 removal of Cyanide d be has been removed is treated with a soluble silver effectedcompound using the amount of silver compound It is preferred as ShOWIl above 130 separate the required completely to precipitate any impurities lactic acid from the precipitate obtained by treat- 40 present. It is usually convenient to remove ment with ferrocyanide before adding silver, but 40 cess nitric acid before treatment with a silver this is not essential. It is further observed that if compound, but if desired, a silver compound may an excess of ferrocyanide is used the treatment be added before removal of excess nitric acid. with silver effects its removal.

Any silver compound may be employed to pre- While We have shown certain specific illustracipitate impurities from lactic acid according to tive examples and conditions herein, it will be 45 I our invention provided of course that the coinunderstood that one skilled in the art may withpound be more soluble than the compound of out departing from the spirit of our invention silver with cyanide. We prefer to usesilverlactate readily devise numerous ways of treating lactic because in this way no objectionable anion is inacid with a soluble silver compound to remove imtroduced into the lactic acid. Other soluble silver purities. 50

compounds which may be used if the anions are We claim: I not so objectionable in a particular instance as 1. In a process for the purification of lactic prohibit their use are silver carbonate, silver aceacid which contains cyanide as an impurity, the tate, and silver sulfate. step comprising adding a soluble silver compound So that our invention may be more fully n rto the lactic acid to precipitate the cyanide. 55

4. In a process for the purification of lactic acid, the step comprising treating the lactic acid with nitric acid, removing the excess nitric acid, and treating the lactic acid with silver lactate.

5. In a process for the purification of lactic acid, the step comprising treating the lactic acid with nitric acid, treating the lactic acid with activated carbon, and treating the lactic acid with silver lactate to efiect substantially complete removal of impurities which are precipitated by silver lactate.

I IVAN L. HAAG.

CHARLES A. VANA. 

